The present invention relates to a automatic cooking appliance which includes a "toast" function. A gas sensor detects gas generated by bread being toasted. Using the gas sensor, a controller can determine the amount of gas driven off from the bread during a predetermined period of time after toasting begins. From this measurement, it can determine whether bread being toasted was initially frozen or at room temperature. Based on this determination, heating can be adjusted to properly toast the bread regardless of its initial state.
It is known to include in a cooking appliance having a toast function a gas sensor for measuring the amount of moisture driven off from bread being toasted in order to determine whether the bread was initially at room temperature or was frozen. The cooking appliance automatically toasts the bread for a time appropriate to the so determined state of the bread.
As a heater heats the bread in the cooking cabinet, it drives moisture from the bread. If the bread is frozen at the time toasting begins, the moisture is locked in the bread as ice. In the first moments of toasting, little moisture will be driven off. Conversely, if the bread is initially at room temperature, considerable moisture will be driven off during the first few moments of toasting.
When the gas sensor detects the increasing rate of the moisture during a predetermined period of time from the starting of the heater, a microprocessor based controller can discriminate the initial condition or state of the bread, i.e., whether it was initially frozen or at room temperature. If the bread were determined to be initially frozen, the cooking appliance would adjust its toasting program to properly toast the initially frozen bread. For example, heat could be applied for a longer time, the temperature could be raised, etc. Thus, regardless of whether the bread was initially frozen or not, it would be properly toasted.
Such appliances operate satisfactorily when they are operated intermittently. However, when such appliances are operated continuously, i.e., to toast one piece of bread after another, the toasting function is not properly adjusted. The problem exists because of residual heat remaining in the cooking cabinet after toasting. As the appliance is used more and more, this residual heat builds up even more. When a slice of bread is put into the cooking cabinet, even though the bread may be frozen, much moisture is driven from it. The cooking appliance is unable to properly discriminate between normal bread and frozen bread. All breads, whether frozen or not, are determined to be initially un-frozen). The cooking appliance may not toast the frozen bread properly.